1. Field of the Invention
This invention relates to a method for placing a perforated liner in a fluid pressurized well, such as a geothermal well. More particularly, the invention relates to such a method involving producing fluids via the well around the outside of the liner while the liner is being placed in the well.
2. Description of the Prior Art
Among the many types of downhole well completions is one in which a preperforated liner or screen is positioned opposite the reservoir interval over which it is desired either to produce fluid or to inject fluid. The liner may be made part of the casing and either left sitting unsupported in the open hole, or the annular space between the wellbore sidewall and the outside of the liner can be filled with a permeable material, such as a gravel pack. Liners can be especially useful where the wellbore sidewall material is poorly consolidated or contains or is composed of shale, clays, silicates and the like and the produced or injected fluids contain or are composed of liquid water. Without a liner being positioned in the wellbore, the shale and other materials tend to swell in the presence of water and slough into the open hole, often leading to collapse of the entire hole. The liner also decreases the amount of formation particles produced along with formation fluids.
Difficulties have been experienced in running preperforated liners into wells, especially wells penetrating reservoirs containing high pressure fluids, more particularly high temperature geothermal fluids and most particularly dry geothermal steam wells. When attempts have been made to run a preperforated liner into such wells, the high pressure formation fluids quickly pass through the perforations and up the liner to the surface where they escape, resulting in considerable danger to the workmen running the liner.
It has been the practice in the past to first inject into the well a fluid, such as water, in sufficient volume to provide a hydrostatic head to counterbalance the formation pressure and "kill" the well. The perforated liner can then be safely run into the well and the injected water subsequently removed. However, this manner of killing the well has not been satisfactory since the reason for running the liner in the first place is that the wellbore may contain shale or similar unstable materials. These materials can swell and collapse into the open hole as soon as contacted by the injected water. Thus, the wellbore becomes restricted with detritus and the liner cannot be lowered into place.
In certain well operations, such as in cementing casing, it is known to run into a well perforated liner whose openings have been filled with plugs, and to later run a cutting tool down the liner to remove the plugs and open the openings in the liner. However, it has not been the practice to employ plugs designed to withstand a differential pressure wherein the pressure on the outside of the liner is considerably greater than the pressure on the inside of the liner.
While the above-described well treating methods have met with some success in particular applications, the need exists for a further improved method for placing a perforated liner in a well.
Therefore, it is a principal object of this invention to provide a method for placing a preperforated liner safely in a fluid pressurized well.
It is a further object to provide such a method operable in wells producing a geothermal fluid.
It is a still further object to provide such a method wherein the well produces dry steam.
It is another object to provide such a method wherein the well is produced while the liner is being placed.
Other objects, advantages and features of this invention will become apparent to those skilled in the art from the following description, drawings and appended claims.